Solid freeform fabrication is a process for manufacturing three-dimensional objects including final products, prototype parts and working tools. Solid freeform fabrication is an additive process in which an object, which is described by electronic data, is automatically built layer by layer from base materials. Several principal forms of solid freeform fabrication are performed using inkjet printing techniques.
In one type of solid freeform fabrication system that uses printing techniques, a number of printed planar layers are combined together to form a planar or non-planar, three-dimensional object. Parts are fabricated by “printing” or ejecting a binder onto a flat bed of powder or slurry brick. Where the binder is ejected, the powder is solidified into a cross section of the object being formed. This printing is performed layer-by-layer, with each layer representing another cross section of the final desired product. Adjacent printed layers are adhered to one another in predetermined patterns to build up the desired product.
In addition to selectively forming each layer of the desired object from the powder in the fabrication chamber, the system can also print a color or color pattern on each layer of the object. Often, the binder is colored such that the functions of binding and coloring are integrated.
For example, inkjet printing technology can be employed in which a number of differently colored inks are selectively ejected from the nozzles of a print head and blended on the build material, e.g., the powder layer, to provide a full spectrum of colors. On each individual layer, conventional two-dimensional multi-pass printing techniques and half-toning algorithms can be used to hide printing defects and achieve a broad range of desired color hues.
In previous solid freeform fabrication systems that use printing technology to add binder to powder, generally the drops of binder are relatively large in order to make the binder flux as high as possible. Binder flux is a measure of how much binder is used in a given period of time. A higher binder flux results in a higher fabrication speed for the solid freeform fabrication system.
However, using large drops of binder makes it difficult or impossible to create small features and smooth surfaces. An object being fabricated may be thought of as being made up of voxels, three-dimensional blocks that each correspond to a drop of binder. The smallest voxel possible is limited by either the powder size or the binder drop size. Because current solid freeform fabrication tools use large drops, the limiting factor on voxel size is usually the binder drop volume.
Therefore, to create objects with fine details, previous solid freeform fabrication systems use small binder drops throughout the entire object. While using small drops may facilitate adding detail to the object and providing a smoother surface finish, the reduction in ink/binder flux results in a slower throughput for the machine and longer fabrication times.